The process of finishing concrete through the concrete curing phases with a self-propelled power trowel is ever changing. Riding power trowels are used for finishing concrete surfaces as the concrete is curing and hardening. A typical riding power trowel is a two-rotor device, with each rotor having a plurality of troweling blades extending out in radial fashion, and usually configured such that the working edge of each blade is in a plane normal to the axis of rotation to provide for smooth and flat finishing of the concrete surface below the riding trowel. There is provided a rigid frame that houses the rotor assemblies, and also an engine, usually a gasoline or diesel engine, which provides the motive power for the rotor assemblies and thus the trowel blades. Atop of the engine and the frame assembly is found an operator's seat and the necessary control systems and levers for operation of the machine. These machines are manufactured in a variety of sizes and weights, with the largest of these machines having not just two, but rather three, rotor and troweling blade assemblies.
For purposes of this prior art section and the entire specification, a two-rotor machine will be used as an example. In two-rotor machines, both rotor assemblies rotate in opposite directions, one to the other. This is shown in FIG. 1.
In FIG. 1, there is shown a two-rotor assembly, wherein each rotor assembly has a gear box, hydraulic drive motor or other means of driving rotation, and troweling blade assemblies that rotate around respective axes of rotation, identified as ARL for the axis of rotation for the left rotor, and ARR as the axis of rotation for the right rotor assembly. Early versions of riding power trowels were mechanically steered. That is, the riding operator manipulated levers that were mechanically connected to the rotors to steer the trowel. But more recent riding trowels utilize hydraulic steering.
The hydraulically controlled steering power trowel is formed of the same basic sub-assemblies, including a rigid frame, engine assembly, operator seat and manual trowel blade pitch control systems, all of which are well known in the art. Also included are left control post and right control post that house, respectively, a left control valve assembly and a right control valve assembly. In a typical device, both the left and right control valve assemblies are proportional pressure output hydraulic valves capable of delivering and maintaining a selectable pressure to a dual-action hydraulic cylinder. U.S. Pat. No. 5,876,740 ('740 patent) discloses a hydraulically controlled steering power trowel, and the '740 patent is incorporated herein by reference. It should be understood that designations “left” and “right,” as used here, are arbitrary; and the functions of what are designated in this disclosure as the “left” and “right” may be accomplished, at the designer's preference, by applying the operable principles to any riding trowel regardless of which of the several assemblies is designated “left” or “right.”
The left control valve assembly is operably interconnected between the frame of the power trowel and the left rotor assembly, and is used to adjust the tilt of the left rotor assembly either inwardly toward the center line of the frame, or outwardly away from the center line of the frame. The left control valve assembly is a single-action proportional pressure output valve that is operable to maintain a selectable hydraulic pressure within one or the other sides of the left dual-action hydraulic cylinder and is operably connected to the left rotor assembly to provide a tilting, either in or out from the center line movement for the left rotor assembly.
Hydraulic power is provided by a standard hydraulic pump that is operably connected to the trowel engine.
Again, only one rotor assembly, which in this example is the left rotor assembly, is only tiltable in and out from the center line. This is achieved by use of a universal drive assembly that is provided to interconnect the output drive shaft of the engine assembly to the rotor assembly. The universal drive assembly is capable of allowing the tilt motion for the left rotor either in or out relative to the center line of the power trowel.
Likewise, the right rotor assembly is interconnected by means of a dual-action universal assembly to the output drive assembly of the engine, and is therefore tiltable not only in an in-and-out direction relative to the center line, but it is also capable of being tilted either in a forward or aft direction. The right rotor assembly is provided with a right lever tilt post and a right forward and aft tilt post. Attached to the right lever tilt post is a dual action right tilt cylinder that is interconnected between the frame and the right tilt lever. In a similar manner, a second dual-action cylinder, the right forward and aft tilt cylinder, is interconnected to the right forward and aft tilt post and is anchored to the frame. The right control valve assembly is a dual action control system, and is operable to maintain a selectable hydraulic pressure in either side of both the right tilt cylinder and the right forward and aft cylinder, thus controlling not only the tilt of the right rotor assembly, but also its forward and aft movement.
Both left and right control valve assemblies are fitted with joysticks that are configured such that if they are pushed forward, both rotor assemblies will tilt inwardly to move the power trowel forward, and conversely, if tilted backward toward the operator, they will operate to tilt the rotors outwardly to move the machine backward. The guidance system just described was fully disclosed in the Applicant's '740 patent. What the prior art lacks, however, is a means to monitor and automatically control the pitch position of the individual troweling blades. The prior art is also without a means of disengaging the pitch actuators to allow the blades to “float” in a flat position.